In a conventional high frequency RFID system comprising at least one RFID reader and multiple RFID transponders (e.g. operating at 13.56 MHz, data transmission from the RFID transponders to the RFID reader via load modulation), a preferably high quality factor of the transponders of the RFID system is aimed to receive electric energy with a high energy level, which electric energy is transmitted from the reader to the transponders. However, disadvantageously, a very high quality factor of the transponders has a negative influence on the whole RFID system insofar, as it makes it difficult to achieve a very high data rate between the transponders and the reader. The reason for this behavior of the RFID system is that increasing the quality factor, or in other words reducing the frequency band width in respect of a given center frequency results in longer swing-out transients of various oscillating circuits employed in the RFID system.
This behavior is shown in the charts of FIGS. 1A to 1D depicting the impulse response E of data signals over time t at an air interface between the reader and the transponders. FIG. 1A shows a low data rate at a high quality factor. It will be appreciated that the envelope Env of the data signal is rather broad indicating a long swing-out transient. FIG. 1B shows a low data rate at a low quality factor resulting in a considerably shortened envelope Env of the data signal providing enough head room between the consecutive data signals for increasing the data rate as is shown in FIG. 1C. However, trying to increase the data rate at the high quality factor of FIG. 1A inevitably results in intersymbol interferences Co1 as depicted in the chart of FIG. 1D. As a consequence, in known RFID systems a compromise between an extent of the quality factor and an intended data rate between the transponder and the reader has to be made.
Further, national and international standards limit both the theoretically available frequency bandwidths and the energy levels of signals being transmitted in the RFID systems, thereby barring a possible solution of this dilemma between quality factors and data rates in RFID systems.
Nevertheless, there is a need for increasing data transmission rates in RFID systems to allow for new applications. An example of such an application might be an electronic passport where fingerprints and other biometric data stored therein have to be transferred to a reading station within the shortest time possible.